1. Field of the Invention
The present invention relates generally to an automatic transmission primarily intended for motor vehicle use, and more particularly, to a method of reducing shift torque from an engine to a transmission that is controlled electronically and hydraulically.
2. Description of the Related Art
Generally speaking, land vehicles require three basic components. These components comprise a power plant (such as an internal combustion engine) a power train and wheels. The power train's main component is typically referred to as the "transmission". Engine torque and speed are converted in the transmission in accordance with the tractive-power demand of the vehicle.
Transmissions are generally referred to as manually actuated or automatic transmissions. Automatic transmissions are designed to take automatic control of the frictional units, gear ratio selection and gear shifting. The control system of the automatic transmission is typically hydraulically operated through the use of several valves to direct and regulate the supply of pressure. This hydraulic pressure control will cause either the actuation or deactuation of the respective frictional units for effecting gear changes in the transmission. However, in recent years, a more advanced form of transmission control system has been proposed, which would offer the possibility of enabling the transmission to adapt itself to changing conditions. An example of such an electronic automatic transmission system is disclosed in U.S. Pat. No. 4,875,391 entitled "An Electronically-Controlled, Adaptive Automatic Transmission System" to Leising et al.
One feature of the above patented automatic transmission system is a method of shift torque management. This feature issued into a corresponding patent, U.S. Pat. No. 4,968,999, entitled "Method of Shift Torque Management for an Electronic Automatic Transmission System" to Fodale et al. The patented method reduced shift torque from the engine to the automatic transmission in response to predetermined conditions existing in the transmission. Although this patented method has worked well, there is still a need in the art to provide more enhanced shift torque management to reduce the input power during the shift to improve clutch durability and shift quality.